High solid epoxy, melamine and isocyanate compositions

ABSTRACT

A low VOC clear coat composition which comprises an epoxy compound, a melamine component and an aliphatic polyisocyanate having an average of 2 to 6 isocyanate functionalities, and optionally contains a catalyst (e.g., organotin catalysts, acid catalysts and combinations); a polyhydroxyl functional compound (e.g., polycarbonate polyol); or other additives (e.g., light absorbers and light stabilizers). Also disclosed is an article coated with the clear coat composition, a process of making the composition, and a process of applying the composition to, for example, an automobile body.

This application is a § 371 of PCT/US00/06960 filed on Mar. 16, 2000which claims benefit of U.S. Provisionals 60/124,850 filed on Mar. 17,1999; 60/131,145 filed on Apr. 27, 1999; and 60/131,146 filed on Apr.27, 1999.

BACKGROUND OF INVENTION

The present invention generally relates to high solids low VOC (volatileorganic component) coating compositions and more particularly to low VOCclear coating compositions suited for multi-layered coatings used inautomotive OEM and refinish applications.

Basecoat-clearcoat systems have found wide acceptance in the past decadeas automotive finishes. Continuing effort has been directed to suchcoating systems to improve the overall appearance, the clarity of thetopcoat, and the resistance to deterioration. Further effort has beendirected to the development of coating compositions having low volatileorganic content (VOC). A continuing need exists for clear coatingformulations which provide an outstanding balance of performancecharacteristics after application, particularly solvent and mar andetch-resistance.

Examples of compositions used to form a protective coatings includethose disclosed in U.S. Pat. No. 4,533,716 (Okoshi et al.). Thesecompositions are prepared using a triazine-type resin formed by aco-condensation reaction with formaldehyde, a polyol, and as required amonohydric alcohol. The polyols used in the condensation reaction may beprepared by an esterification reaction between higher fatty acids andepoxy compounds having a number average molecular weight of 174 to4,000. The polyols used in the U.S. Pat. No. 4,533,716 invention do notinclude epoxy compounds. The U.S. Pat. No. 4,533,716 coatingcompositions are disclosed to include a triazine-type resin and apolyisocianate.

The present invention is directed to a clear coating compositioncomprising isocyanate, melamine, and epoxy components wherein theisocyanate component comprises an aliphatic polyisocyanate having on anaverage 2 to 6 isocyanate functionalities.

The present invention is also directed to a method of producing a clearcoating on a substrate comprising:

applying a layer of a clear coating composition comprising isocyanatemelamine, and epoxy components wherein the isocyanate componentcomprises an aliphatic polyisocyanate having on an average 2 to 6isocyanate functionalities, and curing the layer into the clear coating.

One of the advantages of the present invention is its low VOC,significantly below the current guidelines of Environment ProtectionAgency (EPA) of the United States.

Another advantage is etch and mar resistance of the coating resultingfrom the coating composition of the present invention.

Yet another advantage is the clarity of the coating resulting from thecoating composition of the present invention.

As used herein:

“Two-pack coating composition” means a thermoset coating compositioncomprising two components stored in separate containers. Thesecontainers are typically sealed to increase the shelf life of thecomponents of the coating composition. The components are mixed prior touse to form a pot mix. The pot mix has a limited potlife typically ofminutes (5 minutes to 45 minutes) to a few hours (4 hours to 6 hours).The pot mix is applied as a layer of desired thickness on a substratesurface, such as an autobody. After application, the layer is curedunder ambient conditions or cure-baked at elevated temperatures to forma coating on the substrate surface having desired coating properties,such as high gloss, mar-resistance and resistance to environmentaletching.

“Low VOC coating composition” means a coating composition that includesless then 0.48 kilograms of organic solvent per liter (4 pounds pergallon) of the composition, as determined under the procedure providedin ASTM D3960.

“High solids composition” means a coating composition having solidcomponent in the range of from 65 to 100 percent and preferably greaterthan 70 percent, all in weight percentages based on the total weight ofthe composition.

“Clear coating composition” means a clear coating composition thatproduces upon cure, a clear coating having DOI (distinctness of image)and 20° gloss of more than 70.

“Polymer solids” or “Composition solids” means a polymer or compositionin its dry state.

“Aliphatic” as employed herein includes aliphatic and cycloaliphaticmaterials.

“Crosslinkable” means that the individual components of the adductcontain functionality which react within the composition of theinvention to give a coating of good appearance, durability, hardness andmar resistance.

Applicants have unexpectedly discovered that contrary to conventionalapproaches used in typical thermoset coating compositions, i.e., thoseinvolving a film forming polymer and crosslinking component, a veryviable route lies in a combination of what would traditionally beconsidered crosslinking agents for producing a unique low VOC highsolids clear coating composition which provides coatings with superiorproperties, such as mar and etch resistance.

The clear coating composition includes isocyanate, melamine, and epoxycomponents. The isocyanate component includes an aliphaticpolyisocyanate having on an average 2 to 6, preferably 2.5 to 6 and morepreferably 3 to 4 isocyanate functionalities. The coating compositionincludes in the range of from 35 percent to 70 percent, preferably inthe range of from 40 percent to 65 percent and more preferably in therange of from 45 percent to 60 percent of the aliphatic polyisocyanate,the percentages being in weight percentages based on the total weight ofcomposition solids.

Examples of suitable aliphatic polyisocyanates include aliphatic orcycloaliphatic di-, tri- or tetra-isocyanates, which may or may not beethylenically unsaturated, such as 1,2-propylene diisocyanate,trimethylene diisocyanate, tetramethylene diisocyanate, 2,3-butylenediisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate,2,2,4-trimethyl hexamethylene diisocyanate, dodecamethylenediisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexanediisocyanate, 1,4cyclohexane diisocyanate, isophorone diisocyanate,4-methyl-1,3-diisocyanatocyclohexane, trans-vinylidene diisocyanate,dicyclohexylmethane-4,4′-diisocyanate,3,3′-dimethyl-dicyclohexylmethane4,4′-diisocyanate,meta-tetramethylxylylene diisocyanate, polyisocyanates havingisocyanaurate structural units such as the isocyanurate of hexamethylenediisocyanate and isocyanurate of isophorone diisocyanate, the adduct of2 moles of a diisocyanate, such as hexamethylene diisocyanate,uretidiones of hexamethylene diisocyanate, uretidiones of isophoronediisocyanate or isophorone diisocyanate, and one mole of a diol such asethylene glycol, the adduct of 3 moles of hexamethylene diisocyanate and1 mole of water (available under the trademark Desmodur N of BayerCorporation, Pittsburgh, Pa. or Tolonate HDT-LV from Rhodia Co.,Cranbury, N.J.). If desired, the isocyanate functionalities of thepolymeric isocyanate may be capped with a monomeric alcohol, isopropanolor isobutanol to prevent premature crosslinking in a one-packcomposition. Some suitable monomeric alcohols include methanol, ethanol,propanol, butanol and hexanol.

Some other suitable blockers include lactams, oximes, malonic esters,alkylacetoacetates, triazoles, pyrazoles (e.g. dimethyl pyrazole),phenols and amines. Compositions of the present invention include one ormore melamine. A melamine used in the present invention includes, inpart, alkylated melamine-formaldehyde resin. The alkylated melamineformaldehyde resin maybe partially or fully alkylated. As examples ofpartially alkylated melamines, Cymel 1158 Cymel 324, Cymen 327 (fromCytec Ind., from West Paterson, N.J.), Resimine BM 9539 (from Solutia,Inc., St. Louis, Mo.) can be mentioned. As examples of fully aklykatedmelamines, Cymel 350, and Cymel 301 (from Cytec Co., from Cytec. Ind.,West Paterson, N.J.) and Resimine 764 (from Solutia Inc., St. Louis,Mo.) can be mentioned. A composition of the present invention maycomprise from about 10 weight percent to about 40 weight percent of amelamine, preferably from about 15 weight percent to 35 weight percentof a melamine.

Compositions of the present invention include one or more oligomericepoxy compounds, preferably containing at least two epoxyfunctionalities. Suitable oligomeric epoxy compounds containing ahydroxy functionality or (OH) group used in the practice of the presentinvention include, among others, sorbitol polyglycidyl ether such as DCE358 (form Dixie Chemical Co., Houston, Tex.), diglycerol polyglycidyether such as Denacol EX 421 (from Nagase Cehmical Co., Hyogo, Japan),glycerol polyglycidyl ether such as Denacol Ex 313 and EX 314 (fromNagase Chemical Co., Hyogo, Japan), and triglycidyl tris(2-hydroxyethyl)isocyanurate such as Denacol EX 421 (from Nagase Chemical Co., Hyogo,Japan). Suitable oligomeric epoxy compounds which typically do notcontain significant hydroxy functionality used in the practice of thepresent invention include, among others, di- and polyglycidyl ethers ofpolycarboxylic acid and di- and polyglycidyl ester of acids such asAraldite CY 184 (from Ciba-Geigy, Brewster, N.Y.), cycloaliphaticepoxide such as ERL 4221 (from Union Carbide, Danbury, Conn.), andpolyglycol diepoxide such as DER 736 (from Dow Chemical Co., Midland,Mich.). A composition of the present invention comprises from about 10weight percent to about 40 weight percent of an epoxy compound,preferably from about 15 weight percent to 35 weight percent of an epoxycompound.

The coating composition preferably includes one or more catalysts toenhance crosslinking of the components on curing.

A preferable catalyst is an organotin catalyst such as dibutyltindilaurate, dibutyltin diacetate, dibutyltin oxide, and dibutyltinbis(acetoacetate) in an amount of generally ranges from 0.001 percent to1.0 percent, preferably from 0.01 percent to 0.5 percent and morepreferably from 0.05 percent to 0.2 percent, the percentages being inweight percentages based on the total weight of composition solids.

In addition, the above coating composition can include other suitablecatalysts, such as conventional acid catalysts, for example blocked orunblocked phosphoric acid and sulfonic acid in an amount ranging from0.1 percent to 2 percent, preferably in the range of from 0.2 percent to1.0 percent. As examples of such acid catalysts, phenyl acid phosphate,butyl acid phosphate, octyl acid phosphate, dodecylbenzenesulfonic acid,para-toluenesulfonic acid and dinonylnaphthalene sulfonic acid, whichare optionally blocked with amines such as dimethyl oxazolidine and2-amino-2-methyl-1-propanol can be mentioned.

The coating composition of the present invention, which is formulatedinto high solids coating systems may also contain at least one organicsolvent typically selected from the group consisting of aromatichydrocarbons, such as, petroleum naphtha or xylenes; ketones, such as,methyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone oracetone; esters, such as, butyl acetate or hexyl acetate; and glycolether esters, such as propylene glycol monomethyl ether acetate. Theamount of organic solvent added depends upon the desired solids level aswell as the desired amount of VOC of the composition. If desired, theorganic solvent may be added to both components of the binder. Theamount of organic solvent used results in the composition having a VOCof less than 0.48 kilogram/liter (4 pounds per gallon), preferably inthe range of 0.1 kilogram/liter to 0.4 kilogram/liter (1 pound to 3pounds per gallon) of an organic solvent per liter of the composition.

The coating composition of the present invention may also containconventional additives, such as, stabilizers, and rheology controlagents, flow agents, and toughening agents. Such additional additiveswill, of course, depend on the intended use of the coating composition.Any additives that would adversely effect the clarity of the curedcoating will not be included as the composition is used as a clearcoating. The foregoing additives may be added to either component orboth, depending upon the intended use of the coating composition.

To improve weatherability of the clear finish of the coatingcomposition, about 0.1-5%, by weight, based on the weight of thecomposition solids, of an ultraviolet light stabilizer or a combinationof ultraviolet light stabilizers may be added. These stabilizers includeultraviolet light absorbers, screeners, quenchers and specific hinderedamine light stabilizers. Also, about 0.1-5% by weight, based on theweight of the composition solids, of an antioxidant can be added.Typical ultraviolet light stabilizers that are useful includebenzophenones, such as hydroxydodecyclbenzo-phenone,2,4-dihydroxybenzophenone; triazoles, such as2-phenyl4-(2′-4′-dihydroxybenzoyi)triazoles; and triazines, such as3,5-dialkyl-4-hydroxyphenyl derivatives of triazine and triazoles suchas 2-(benzotriazole-2-yl)-4,6-bis(methylethyl-1-phenyl ethyl)phenol,2-(3-hydroxy-3,5′-di-tert amyl phenyl) benzotriazole,2-(3′,5′-bis(1,1-dimethylpropyl)-2′-hydroxyphenyl)-2H-benzotriazole,benzenepropanoic acid,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)4-hydroxy-,C7-9-branchedalkyl esters, and2-(3′,5′-bis(1-methyl-1-phenylethyl)-2′-hydroxyphenyl)benzotriazole.

Typical hindered amine light stabilizers arebis(2,2,6,6-tetramethylpiperidinyl)sebacate,bis(N-methyl-2,2,6,6-tetramethylpiperidinyl)sebacate andbis(N-octyloxy-2,2,6,6-tetramethylpiperidynyl)sebacate. Particularlyuseful blend of ultraviolet light absorbers and hindered amine lightstabilizers is bis(N-octyloxy-2,2,6,6-tetramethylpiperidynyl)sebacateand benzenepropanoic acid,3-(2H-benzotriazol-2-yl)-5(1,1-dimethylethyl)4hydroxy-,C7-9-branchedalkyl esters.

The coating composition of the present invention optionally contains, inthe range of 0.5 weight percent to 15 weight percent, preferably 1weight percent to 10 weight percent of polyhydroxy functional compoundssuch as polycarbonate polyol (formula shown in the example),2-ethyl-1,3-hexanediol, polycaprolactone triol, and the adduct ofepsilon caprolactone and 1,3,5-tris(2-hydroxyethyl) cyanuric acid, allpercentages being based on the total weight composition solids.

The coating composition of the present invention optionally contains inthe range of from 0.5 percent to 30 percent, preferably in the range offrom 1 percent to 20 percent, stabilized crosslinked polymer particles,i.e., non-aqueous dispersion (NAD) (as described in detail in U.S. Pat.No. 4,960,828), all percentages being based on the total weight ofcomposition solids.

The clear coating composition of the present invention may be suppliedin the form of a two-pack coating composition in which a first packincludes the polyisocyanate and a second-pack includes the melamine,epoxy compounds and other additives.

Generally, the first and the second pack are stored in separatecontainers and mixed before use. The containers are preferrably sealedair tight to prevent reactions during storage.

Alternatively, when the isocyanate functionalities of the polyisocyanateare blocked, all components of the composition can be stored in the samecontainers in the form of a one-pack coating composition.

In use, the first-pack of the two-pack coating composition containingthe polyisocyanate and the second-pack containing the melamine, epoxycompounds, and other additiaves are mixed just prior to use for about 1to 15 minutes before use to form a pot mix, which has limited pot life,in range of from 5 minutes to 6 hours, before it becomes too viscous topermit application through conventional application systems, such asspraying. Alternatively, the first pack and the second pack are mixedtogether at the plural spray gun with or without electrostastics, beforeapplied to a substrate. Other methods of applications include rollercoating, dipping or brushing and other conventional application methods.The layer of the coating composition then cures under ambient conditionsor preferably at higher temperatures in the range of 80-160° C. for 10minutes to 3 hours, preferably in the range of 20 minutes to 1 hour toform a coating on the substrate having the desired coating properties.

When the one-pack coating composition containing the blockedpolyisocyanate is used, a layer thereof applied over a substrate usingaforedescribed application techniques, is cured at a baking temperaturein the range of from 80° C. to 200° C., preferably in the range of 80°C. to 160° C., for about 10 to 60 minutes It is understood that actualbaking temperature would vary depending upon the catalyst and the amountthereof, thickness of the layer being cured, the blocked isocyanatefunctionalities and the melamine utilized in the coating composition.The use of the foregoing baking step is particularly useful underOriginal Equipment Manufature (OEM) condition.

It is understood that the actual curing time depends upon catalyst typeand amount, the thickness of the applied layer and on the presence orabsence of any suitable drying devices, such as, fans that assist incontinuously flowing air over the coated substrate to accelerate thecure rate. Generally, a clearcoat layer having a thickness in the rangeof from 25 micrometers to 75 micrometers applied over a metal substrate,such as automotive body which is often precoated with other coatinglayers such as electrocoat, primer and basecoat; cures in 20 to 60minutes at at about 80° C. to 160° C.

Testing Procedures

The following test procedures were used for generating data reported inthe examples below:

Test Test Method Dry film thickness ASTM D1400 Appearance ASTM D523,VISUAL 20° Gloss ASTM D523 DOI ASTM D5767 Tukon Hardness ASTM D1474 Marresistance ASTM D5178 Percent solids ASTM D2369

EXAMPLE

The following non-limiting examples will further illustrate theinvention. All parts, percentages, ratios, etc., in the examples are byweight unless otherwise indicated. The following abbreviations listed inTable 1 are used throughout. The examples below are carried out usingstandard techniques, which are well known and routine to those skilledin the art, except where otherwise described in detail. These examplesare illustrative, but do not limit the invention.

Definitions

ARALDITE CY 184 Oligomeric, Epoxy Resin, 100% Solid (Ciba-Geigy,Brewster, NY) CYMEL 1158 Polymeric Melamine, 80% Solid (Cytec Co., WestPaterson, NJ) TINUVIN 384 Ultraviolet Light Screener, 100% Solid(Ciba-Geigy, Tarrytown, NY) TINUVIN 292 Hindered Amino Light Stabilizer(Ciba- Geigy, Tarrytown, NY) BYK 301 Flow Additive (Byk Chemie USA,Wallingford, CT) Dibutyltin Dilaurate Catalyst (from Air Products,Allentown, PA) Phenyl Acid Phosphate Catalyst (from Albright & WilsonCo., Glen Allen, VA) 2-Ethylhexyl Acetate Solvent (from Eastman ChemicalCo., Kingsport, TN) TOLONATE HDT-LV Isocyanate Timer, 100% Solid (fromRhodia Inc., Cranbury, NJ) CYMEL 350 Monomeric Melamine 100% Solid(Cytec Co. West Paterson, NJ) ERL 4221 Oligomeric Epoxy resin, 100%solid (Union Carbide, Danbury, CT) Dodecylbenzenesulfonic acid Catalyst(Kings Industry, Norwork, CT) salt of amionethyl-proponol DER 736Oligomeric Epoxy Resin, 100% solid (Dow Chemical Co. Midland, MI)

Synthesis Example 1 Synthesis of Polycarbonate PL1015

A 5 liter round bottom flask was fitted with stirrer, condenser, heatingmantle, thermometer, and Dean Stark trap. To the reactor were charged402.5 gm tromethylolpropane, 501.6 gm neopentylglycol, 567.2 gm1,6-hexanediol, 1063.2 gm diethylcarbonate, and 0.2 gmdibutyltindilaurate (all available from Aldrich Chemicals, Milwaukee,Wis.). The mixture was slowly heated under agitation until ethanol beganto distill off at approximately 120° C. Temperature was allowed toslowly increase to 140° C. Distillation continued at 140° C. for a totalof 16 hours until 829.3 gm ethanol were removed. The material was thencooled and 89.8 gm methylamyl ketone was added. The reaction yielded1707.2 grams of polycarbonate polyol at 94.2% weight percent solids.

Protective Coating Example 1

Part A was prepared by combining the following ingredients: 20 parts ofARALDITE CY 184; 25 parts of CYMEL 1158; 2.0 parts of TINUVIN 384; 1.5parats of TINUVIN 292; 0.68 parts of a solution comprising 10 weightpercent of BYK 301 in propylene monoetheyl ether acetate; 5.0 parts of asolution of 1 weight percent of dibutyltin dilaurate in butyl acetate;0.67 parts of a solution of 75 weight percent of phenyl acid phosphatein butanol; 2.0 parts of PL1015, and 5.26 parts of 2-ethylhexyl acetate.This mixture was then combined with 54.7 parts of TOLONATE HDT-LV as apart B to form a clear composition.

Separately, a steel substrate, which had been precoated with electrocoatand primer was coated with a conventional waterborne bascoat to athickness of 15 micron and prebaked at 82° C. for 10 minutes. Then, theabove clear composition was sprayed over the above prebaked waterbornebasecoat and baked at 140° C. for 30 minutes.

The substrate was cooled and Protective Coating 1 was tested.Characteristics of Protective Coating 1 are illustrated in Table 1 ascompared to a characteristics of Control Protective Coating(conventional 2K isocyanate/acrylic polyol clear composition which hadbeen prepared similarly).

TABLE 1 CHARACTERISTICS OF PROTECTIVE COATINGS Control Coating sampleProtective Coating 1 [acrylic polyol/iso) % Solid 85.6 53.0 VOC(lbs/gal) 1.29 3.9 #4 Ford spray viscosity (sec) 100 30 Gloss (20 deg.)95 89 DOI 97 97 Tukon hardness (Knoop) 13.3 11.1 Cleveland humidity (96hour @ 60 C.) Tape adhesion No failure No failure Blister No No Boilingwater resistance (3 h) Tape adhesion No failure No failure blister No NoGravel @ −20 deg. C. 7 6 (Note 1) Percent gloss retention after 96 91dry mar (note 2) Min. temp. (C.) without spot 65 60 of synthetic acidrain soln. (Note 1) Rating based on 1-10 with 10 best (Note 2) Glossretention after 10 rubbing cycles using an abrasive material

As shown in Table 1, Clearcoat Example 1 clearly showed good appearanceat very low VOC and gave good physical properties.

Protective Coating Example 2

Protective Coating 2 was prepared as follows: Parts A was prepared bycombining 22.0 parts of ARALDITE CY 184, 25.0 parts of CYMEL 1158, 2.0parts of TINUVIN 384, 1.5 parts of TINUVIN 292, 0.68 parts of a solutionof 10 weight percent of BYK 301 in propylene ethyl ether acetate, 5.0parts of a solution of 1 weight percent dibutyltin dilaurate in butylacetate, 0.67 parts of a solution of 75 weight percent of phenyl acidphosphate in butanol and 5.26 parts of 2-ethylhexyl acetate. The abovepart A mixture was then combined with 54.7 parts of TOLONATE HDT-LV as apart B to form a clear composition. The composition had a solid contentof 85.6 weight percent, and a volatile organic compounds concentrationof 1.29 lbs/gal. (0.15 Kg/liter).

The composition was then sprayed over a conventional silver metallicwaterborne basecoat which had been applied to the similar substrate asdescribed in Example 1 and prebaked at 82° C. for 10 minutes, and bakedat 140° C. for 30 minutes similar to Example 1. The coating exhibitedgloss 95, DOI 95 and Tukon hardness 11.3.

Protective Coating Example 3

Protective Coating 3 was prepared as follows: Part A was prepared bymixing20.0parts of ARALDITE CY 184, 12.5 parts of CYMEL 1158, 10.0 partsof CYMEL 350, 2.0 parts of TINUVIN 384, 1.5 parts of TINUVIN 292, 0.68parts of a solution of 10 weight percent of BYK 301 in propylenemonoetheyl ether acetate, 0.5 parts of a solution of 10 weight percentof dibutyltin dilaurate in Butyl acetate, 0.67 parts of a solution of 75weight percent of phenyl acid phosphate in butanol, 2.0 parts of PL1015and 10.26 parts of 2-ethylhexyl acetate. This part A mixture was thencombined with 54.7 parts of TOLONATE HDT-LV as part B to form a clearcomposition. The clear composition had a solid content of 87.1 weightpercent, and a volatile organic compounds concentration of 1.18 lbs/gal.(0.14 Kg/liter).

The composition was then sprayed over a conventional silver metallicwaterborne basecoat which had been applied to the similar substrate asdescribed in Example 1 and prebaked at 82° C. for 10 minutes, and bakedat 140° C. for 30 minutes similar to Example 1. The coating exhibitedgloss 94, DOI 94 and Tukon hardness 11.4.

Protective Coating Example 4

Protective Coating 4 was prepared as follows: Part A was prepared bymixing 20 parts of ERL 4221, 25 parts of CYMEL 1158, 2.0 parts ofTINUVIN 384, 1.5 parts of TINUVIN 292, 0.68 parts of a solution of 10weight percent of BYK 301 in propylene monoethyl ether acetate, 0.5parts of a solution of 10 weight percent dibutyltin dilaurate in butylacetate, 1.4 parts of dodecylbenzenesulfonic acid salt ofamionethylpropanol, 2.0 parts of PL 1015, and 5.26 parts of 2-ethylhexylacetate. This part A mixture was then combined with 54.7 parts ofTOLONATE HDT-LV as a part B to form a clear composition. The clearcomposition had a solid content of 88.44 weight percent, and a volatileorganic compounds concentration of 1.05 lbs/gal (0.12 Kg/liter).

The composition was then sprayed over a conventional silver metallicwaterborne basecoat which had been applied to the similar substrate asdescribed in Example 1 and prebaked at 82° C. for 10 minutes, and bakedat 140° C. for 30 minutes similar to Example 1. The coating exhibitedgloss 90, DOI 90 and Tukon hardness 4.6.

Protective Coating Example 5

Protective Coating 5 was prepared as follows: Part A was prepared bymixing 20.0 parts of DER 736 20.0 parts of CYMEL 350, 2.0 parts ofTINUVIN 384, 1.5 parts of TINUVIN 292, 0.68 parts of a solution of 10weight percent BYK 301 in propylene monoetheyl ether acetate, 6.0 partsof the salt of dodecylbenzenesulfonic acid and diethanolamine, 4.2 partsof PL 1015 and 6.75 parts of 2-Ethylhexyl Acetate. This part A mixturewas then combined with 52.5 parts of TOLONATE HDT-LV as a part B to forma clear composition. The composition had solid content of 88.0 weightpercent, and a volatile organic compounds concentration of 1.09lbs/gal.(0.13 Kilograms/liter).

The composition was then sprayed over a conventional silver metallicwaterborne basecoat which had been applied to the similar substrate asdescribed in Example 1 and prebaked at 82° C. for 10 minutes, and bakedat 140° C. for 30 minutes similar to Example 1. The coating exhibitedgloss 87, DOI 90 and Tukon hardness 3.6.

The complete disclosures of all patents, patent applications, andpublications are incorporated herein by reference as if individuallyincorporated. Various modifications and alterations of this inventionwill become apparent to those skilled in the art without departing fromthe scope and spirit of this invention, and should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

1. A low VOC clear coating composition comprising isocyanate, epoxycompound and melamine components wherein said isocyanate componentcomprises an aliphatic polyisocyanate having an average of 2 to 6isocyanate functionalities.
 2. The composition of claim 1 wherein saidcomposition further comprises a catalyst.
 3. The composition of claim 2wherein said catalyst is selected from the group consisting of anorganotin catalyst, acid catalyst and combinations thereof.
 4. Thecomposition of claim 3 wherein said organotin catalyst is selected fromthe group consisting of dibutyltin diacetate, dibutyltin dilaurate,dibutyltin oxide, dibutyltin bis(acetoacetate) and combinations thereof.5. The composition of claim 3, wherein said acid catalyst is selectedfrom the group consisting of phenyl acid phosphate, butyl acidphosphate, octyl acid phosphate, dodecylbenzenesulfonic acid,paratoluenesulfonic acid, dinonylnaphthalenesulfonic acid andcombinations thereof.
 6. The composition of claim 3 or 5, wherein saidacid catalyst is blocked with an amine.
 7. The composition of claim 6,wherein said amine is dimethyloxazolidine, 2-amino-2-methyl-1-propanol,di(2-hydroxyethyl)amine or a combination thereof.
 8. The composition ofclaim 6, wherein said composition comprises about 0.001 weight percentto about 3.0 weight percent of catalyst, all percentages based on thetotal weight of composition solid.
 9. The composition of claim 2,3,4, or5 wherein said composition comprises about 0.001 weight percent to about3.0 weight percent of catalyst, all percentages based on the totalweight of composition solid.
 10. The composition of claim 1 furthercomprises a polyhydroxyl functional compound.
 11. The composition ofclaim 10 wherein said polyhydroxyl functional compound is apolycarbonate polyol.
 12. The composition of claim 10 or 11 wherein saidpolyhydroxyl functional compound comprises from about 0.5 weight percentto about 15 weight percent of the composition.
 13. The composition ofclaim 1 further comprises a non-aqueous dispersion resin.
 14. Thecomposition of claim 1, wherein said epoxy compound is selected from thegroup consisting of a polyglycidyl ester of an acid, a polyfunctionalaliphatic epoxy compound, a cycloaliphatic epoxy compound, apolyfunctional cycloaliphatic epoxy compound or combinations thereof.15. The composition of claim 1, or 14, wherein said epoxy compoundcomprises from about 10 weight percent to about 40 weight percent of thecomposition.
 16. The composition of claim 1 or 14, wherein said epoxycompound is a di or polyglycidyl ester of a di or polycarboxylic acid.17. The composition of claim 16, wherein said epoxy compound comprisesfrom about 10 weight percent to about 40 weight percent of thecomposition.
 18. The composition of claim 1, wherein said melamine is afully alkylated melamine-formaldehyde resin.
 19. The composition ofclaim 1, wherein said melamine is a partially alkylatedmelamine-formaldehyde resin.
 20. The composition of claim 1, 18 or 19,wherein said melamine compound comprises from about 10 weight percent toabout 40 weight percent of the composition.
 21. The composition of claim1 further comprises ultraviolet light absorbers, light stabilizers or acombination thereof.
 22. The composition of claim 1, wherein saidaliphatic polyisocyanate is selected from the group consisting of timersof hexamethylene diisocyanate, isophome diisocyanate, ormeta-tetramethylene diisocyanate and combinations thereof.
 23. Thecomposition of claim 1 or 22, wherein said aliphatic polyisocyanate isblocked.
 24. The composition of claim 23, wherein aliphaticpolyisocyanate is blocked by reacting with an aliphatic mono-alcohol.25. The composition of claim 23, wherein said aliphatic polyisocyanatecomprises from about 35 weight percent to about 70 weight percent of thecomposition.
 26. The composition of claim 1, or 22, wherein aliphaticpolyisocyanate is blocked by reacting with an aliphatic mono-alcohol.27. The composition of claim 1, or 22, wherein said aliphaticpolyisocyanate comprises from about 35 weight percent to about 70 weightpercent of the composition.
 28. The composition of claim 1 furthercomprises a solvent.
 29. The composition of claim 1, wherein saidcomposition has a solids content of greater than 65 weight percent. 30.A composition of claim 1, wherein said composition has a solids contentof greater than 80 weight percent.
 31. An article comprising a substratehaving a first and a second major surface and a layer of protectivecoating, the protective coating comprising a hardened composition ofclaim
 1. 32. The article of claim 31, wherein said substrate is selectedfrom the group consisting of metal, plastic, wood and rubber.
 33. Thearticle of claim 31, wherein said layer of protective coating has athickness of about 25 micrometers to about 75 micrometers.
 34. Thearticle of claim 31, wherein said layer of protective coating isacid-resistant.
 35. The article of claim 31, wherein said layer ofprotective coating is transparent.
 36. The article of claim 31,comprising a layer of electrocoat, primer and a layer of basecoatinterposed between the substrate and the layer of protective coating.37. A process of making a clear coating composition that upon hardeningforms a clear protective coating comprising the steps of: combining analiphatic polyisocyanate having an average of 2 to 6 isocyanatefunctionalities an epoxy compound, and melamine.
 38. A process of makinga clear coating composition that upon hardening forms a protectivecoating comprising the steps of: making a first mixture comprising anepoxy, a melamine; making a second mixture comprising an aliphaticpolyisocyanate having an average of 2 to 6 isocyanate functionalities;and combining the first and second mixtures.
 39. The process of claim38, wherein said first mixture, second mixture or both mixtures containa solvent.
 40. A clear coating composition produced by the process ofclaim
 38. 41. A process of making an article comprising the steps of:applying a clear coating composition comprising an aliphaticpolyisocyanate having an average of 2 to 6 isocyanate functionalities,an epoxy compound, and melamine to a substrate; and hardening thecomposition.
 42. The process of claim 41, wherein said composition isapplied by spraying.